Change the following statement into passive voice.
Do you understand what I mean?
A) What I mean is that understood by you?
B) Was what I mean understood by you?
C) Is what I mean understood by you?
D) What I mean is understood by you?

Hint: While converting an interrogative sentence from the active voice to the passive voice the auxiliary verbs ‘do, does, or did’ should never be used. Question words like ‘when, why, how, where and what do not change their position or form when they are in the beginning of the sentence. However, words like, ‘who’ is changed to ‘by whom’, and ‘whom’ is changed to ‘who’.

Complete answer:
To change the given sentence into its passive form, you need to take the subject from the active voice (you) and make it the object in the passive voice. Then we take the object from the active voice (what I mean) and make it the subject of the passive voice.

Now let us check the options.
Option A) What I mean is that understood by you – In this option the subject and the verbs have been interchanged correctly, but there has been an unnecessary use of the word ‘that’ to refer to the subject. We do not need an extra word to indicate the subject in a sentence where we already have a subject. Thus, this option is incorrect.
Option B) Was what I mean understood by you – Here, the subject and the object have been interchanged correctly, the verb ‘understood’ is in the correct form and the sentence is grammatically correct. The sentence in the question is the present tense, but here the word ‘was’ indicates that this option is in the past tense. Therefore, this option is incorrect.
Option C) Is what I mean understood by you – Here, the subject-object interchanging has been done correctly. The verb ‘understood’ has been used in the correct form. The word ‘is’ indicates the present tense of the sentence as that of the sentence in the question. Therefore, this option is absolutely correct.
Option D) What I mean is understood by you – This option seems very similar to option (C). The difference is that the verb ‘be’ has been used after the subject. While asking a question, the question should always begin with the ‘be’ verb. It could be ‘is, was, am’ etc. in this case it is ‘is’. Therefore this option is incorrect.

Thus, the correct answer is Option (C) Is what I mean understood by you?

Note: The passive voice is used to write a sentence, when (i) we do not know what or who the subject is, (ii) the subject is too obvious, or (iii) the subject is just not important in that particular scenario. For e.g. “The cat ate the rat” is a sentence in the active voice. Here the cat is important and is the subject. But in a case where the rat is important, we would use a passive voice. For e.g. “The rat was eaten by the cat.” Now the cat is not important, and the focus of the sentence has changed from the cat to the rat.